Sustainable Aquaculture

Shrimp

a. Water temperature

Optimal range:

Vannamei: 25-32°C; temperatures below 20°C slow growth, and temperatures above 35°C increase stress and disease risk.

Seasonal influence:

Tropical regions: year-round culture, 2-3 cycles per year (80-100 days each).
Temperate regions: single summer cycle (100-120 days) or greenhouse-assisted winter cycle (additional 10-20 days for heating).

b. Farming system

System Strength Cycle (days) Survival rate Advantages/disadvantages.
Traditional earthen pond Low/Medium 100-120 60-70% Low cost, natural ecosystem; susceptible to environmental fluctuations.
High-density concrete/tile pond High 80-90 70-80% Better water control, faster growth; higher investment.
Recirculating aquaculture system (RAS) Industrial 70–80 80–90% Shortest cycle, year-round production; high-tech, energy-saving and environmentally friendly.
Biofloc system Innovative 85–95 75–85% Low water exchange, suitable for inland areas; requires strict nutrient management.

2. Typical cycle stages (taking the cultivation of Penaeus vannamei in high-position ponds as an example)

a. Nursery stage (0-30 days)

Hatching stage (0-10 days):
Larvae (nauplii) develop to post larvae (PL10, about 0.5 cm) in a controlled hatchery using sterile seawater and algae/biofeed.
Nursery/early growth stage (10-30 days):
PL10 are transferred to nursery ponds/tanks and fed a high protein feed (protein content 40-45%) and grow to 3-5 cm (PL30-PL40).
Survival rate: Survival rate can reach 85-90% due to strict biosecurity and water quality control.
b. Grow-out to market size (harvest in 30 days)

Stocking density:
High density system: 100-150 shrimp/m2 (target 30-40 g in 80-90 days).
Low density system: 30-50 shrimp/m2 (larger size, 40-50 g, achieved in 100-110 days).
Feeding regimen:
Postlarvae (3-5 cm): 5-6 feeds per day, 5-8% of body weight, 40% protein.
Grow-out (5-10 cm): 3-4 feeds per day, 3-5% of body weight, 32-35% protein.
Feed conversion ratio (FCR): 1.0-1.5 for industrial systems; 1.8-2.0 for conventional ponds.
Water quality management:
Dissolved oxygen ≥ 4 mg/l (through aeration), pH 7.5-8.5, ammonia/nitrite < 0.1 mg/l.
Perform regular water changes (20-30% daily in ponds, 10-15% daily in recirculating water systems) to control pollutants.
c. Harvest time

Market size:
Live/chilled market size: 30-40 g (80-100 shrimp/kg) - 80-90 days.
Frozen/processed market size: 40-60 g (50-80 shrimp/kg) - 100-120 days (P. monodon: 60-100 g, 120-150 days).
Partial harvest: In some systems, selective harvesting of large individuals allows smaller shrimp to grow further, thus reducing overall cycle variation.

3. Regional and system-specific period differences

a. Tropical vs. Temperate

Tropical:
Open ponds have two full cycles per year (80-100 days each); RAS systems can have three cycles per year (70-80 days each).
Temperate:
Summer single cycle (100-120 days) without heating; winter cycle in greenhouses can be extended to 120-140 days due to slower growth.
b. Saltwater aquaculture vs. freshwater aquaculture

Saltwater (coastal ponds): slightly faster growth (due to optimal salinity of 15-25 ppt) - growth rate of whiteleg shrimp is 85-95 days.
Freshwater (inland ponds/RAS systems): growth rate is about 5-10% slower (osmotic pressure) - growth rate of whiteleg shrimp of the same size is 95-105 days.

4. Strategies to optimize the breeding cycle

a. Genetic Improvement

Use SPF/SPR (Specific Pathogen Resistance) strains to reduce disease downtime (e.g., EHP and WSSV resistant strains of P. vannamei).
Hybrid vigor (e.g., P. vannamei × P. stylirostris) can increase growth rates by 10-15%.
b. Environmental Control

Temperature Regulation:
In temperate regions, using geothermal water or solar panels to maintain temperatures at 25-30°C can reduce the culture cycle by 10-15 days.
Salinity Management:
Gradual acclimatization to salinity in freshwater systems to minimize stress and improve feed efficiency.
c. Nutrition and Feeding

Compounded Feed: High-quality pelleted feed with added enzymes/probiotics to improve digestion (can reduce feed conversion by 0.1-0.2).
Feeding Frequency: In industrial systems, feed 4-6 times a day using automatic feeders to maximize nutrient absorption during peak activity (morning/evening).
d. Disease prevention

Biosecurity: quarantine of shrimp seed, disinfection of ponds between culture cycles, and use of probiotics (e.g. Lactobacillus) to suppress pathogens.
Early warning system: regular PCR testing for viruses (WSSV, EHP) to eliminate infected ponds as early as possible to avoid culture cycle failure.
e. Harvest management

Specific size harvesting: use of mesh nets to preferentially harvest marketable size shrimp, allowing smaller shrimp to grow without density pressure (average cycle shortened by 5-10 days).

Tilapia

1. Main influencing factors

a. Water temperature

Suitable temperature range: Tilapia is a tropical/subtropical fish that thrives at temperatures between 25-32°C. Growth stagnates below 15°C and mortality occurs below 10°C.
Regional differences:
Tropical/subtropical regions: Year-round warm waters allow tilapia to grow from fry to market size (500-1,000 g) in 5-6 months.
Temperate regions: Shorter warm seasons (5-10 months) extend the growth period to 7-8 months; greenhouses or indoor facilities are required during winter to avoid mortality.
b. Breeds and strains

Fast-growing strains (e.g. GIFT tilapia, Nile × Blue tilapia hybrid): Due to selective breeding, tilapia can reach market size in 5-6 months.
Traditional strains (e.g. Nile tilapia): Slightly slower growth, requiring 7-8 months to reach the same size.
c. Culture systems

Pond culture (most common):
Extensive/low density: 7-8 months (yield: 800-1,000 kg/ha).
Intensive/high density: 5-6 months with strict feeding and water quality management (yield: 2,000-3,000 kg/ha).
Cage/raft culture (lake/deep sea): Faster growth (5-6 months) due to high dissolved oxygen and high water flow.
Recirculating aquaculture system (RAS): Minimum cycle of 4-5 months by controlling temperature and water quality, but initial investment is higher.

2. Typical cycle stage (intensive pond mode)

a. Fry to fingerling stage (0-30 days)
Fry (0.5-1 cm) produced in hatcheries are grown to fingerling size (5-10 cm) in nursery ponds. Survival rate: 80-90%.
b. Growing to market size (harvest at 30 days)
Low-density polyculture: 7-8 months, stocking 1000-1500 fry per hectare (polyculture of carp, catfish).
High-density monoculture: 5-6 months, stocking 2500-3000 fry per hectare. Regular sorting (to avoid individual differences) and intensive feeding can accelerate growth.
Harvest threshold: Most markets accept fry above 500 g, and some regions prefer larger sizes (above 1000 g). Partial harvesting (selective fishing) can shorten the overall harvest cycle of remaining fry.

3. Comparison of different farming system cycles

Culture system Temperature control cycle (months) Market size (grams) Advantages
Ponds (intensive) Natural culture 5–6 500–1,000 Low cost, scalable
Cage culture (warm water) Natural culture 5–6 600–1,200 Fast growth, depending on water quality
RAS (industrial) Artificial culture 4–5 500–800 Year-round production, shortest cycle
Northern ponds (extensive) None 7–8 500–800 Suitable for short warm seasons

4. Strategies to shorten production cycles

Strain selection: Use fast-growing hybrids (e.g. GIFT, Nile salmon × Golden River salmon) to shorten the cycle by 1-2 months.
Temperature management:
In temperate regions, deploy greenhouses or geothermal heating to extend the growing season.
Keep water temperature within the optimal range to ensure continuous feeding and growth.
Nutrition and feeding:
Fry/juveniles are fed a high-protein diet (32-35% protein content), and adult fish are fed a 28-30% protein diet to optimize feed conversion (FCR: 1.2-1.4).
Feed frequently (2-3 times/day) to maximize nutrient absorption.
Water quality optimization:
Ensure dissolved oxygen ≥ 4 mg/L and pH 7.5-8.5 through aeration and probiotics to reduce stress and disease risks.
Conclusion
The production cycle of tilapia is usually 4-8 months, depending on environmental conditions and culture methods. Intensive farming systems are used in tropical regions with the shortest production cycles (5-6 months), while temperate regions require longer cycles or supplemental heating. Strategic selection of fish species, temperature control and efficient management can significantly increase growth rates and shorten harvesting time.

Sea Bass

1. Reproduction stage

Objective: Produce high-quality eggs and juveniles.
Process:
Select mature broodstock (3-5 years old, 1-3 kg body weight) with the best genetic traits.
Simulate natural spawning conditions (e.g., controlled photoperiod, water temperature 14-18°C, salinity 30-35 ppt).
Spawning occurs in winter and spring, with females producing 500,000-2 million eggs per kg body weight.
Duration: Management throughout the year, with the spawning season lasting 2-3 months.

2. Incubation

Stage 1: Egg incubation
The fertilized eggs are incubated in a 16-19°C tank for 36-48 hours until they hatch.
Survival rate: about 50-70% (depending on egg quality and water quality).
Stage 2: Larval rearing
Newly hatched larvae (0.3-0.5 cm) are fed with live food (rotifers, copepods, Artemia) for 4-6 weeks.
As their digestive system develops functionally, they are gradually transitioned to artificial feed.
Water quality is critical (water temperature 18-22°C, salinity 25-35 ppt, high oxygen environment > 5 mg/L).
Stage 3: Juvenile production
Juveniles metamorphose into juveniles (2-5 cm) in 6-8 weeks and are available for nursery or direct stocking.
Incubation period: 8-12 weeks, producing juveniles 3-5 cm.

3. Seedling stage (optional for small farms)

Objective: To grow fingerlings into larger fish (8-15 cm) to improve their survival in grow-out systems.
Rearing conditions:
Shallow ponds/ponds with low salinity (15-25 ppt) or brackish water.
Feeding 3-4 times daily with commercial pelleted feed (25-50% protein).
Duration: 4-8 weeks, depending on growth rate and target size.

4. Development stage

This is the longest phase, during which the fish are raised to marketable size (400-600 g for a whole fish, 1-2 kg for fillets).
Farming methods and duration:
Marine cage culture (most common):
Deployed in coastal waters (salinity 20-35 ppt, water temperature 15-25°C).
Stocking density: 15-30 fish/m3 (depending on water flow and oxygen content).
Feeding 2-3 times a day with a high-protein pelleted feed (protein content 40-45%), with a feed conversion ratio (FCR) of about 1.2-1.5.
Duration: 12-18 months (growth is faster in warm climates, slower in colder regions).
Pond/brackish water culture:
Suitable for areas with suitable estuarine environments (salinity 5-25 ppt).
Stocking density: 10-20 fish/m2, growth is slightly slower than cage culture due to fluctuations in water quality.
Duration: 14-20 months.
RAS:
Controlled indoor environment with good water quality (adjustable salinity, water temperature 20-24°C).
High stocking density (30-50 kg/m3), precision feeding and shorter cycles.
Duration: 10-14 months (optimal conditions accelerate growth).
Key growth factors:
Temperature: Optimal growth is 20-25°C; growth slows below 15°C or above 30°C.
Feeding: Feed regularly (adjusted according to water temperature and fish size) to maximize feed conversion ratio (FCR).
Health management: Prevention of diseases (e.g. vibriosis, nematodes) through biosecurity and vaccination.

5. Harvest

Size: Typically 400-600 g for fresh market, 1-2 kg for processed fillets.
Methods: Netting (cages), drained ponds or automated RAS systems.
Survival: 70-85% from juvenile to harvest, depending on management practices.
Overall production cycle summary
Phase Duration Main output
Broodstock and spawning Year-round (spawning period: 2-3 months) Fertilized eggs/larvae
Hatchery and nursery 12-20 weeks Juveniles (3-15 cm)
Grow-out 10-18 months Marketable size sea bass (400 g - 2 kg)
Total cycle 14-24 months Depends on culture practices and climate
Key considerations
Seasonality: Growth is fastest in warm seasons; slower growth in winter may extend the cycle in temperate regions.
Cost and profitability: Initial investments in fingerlings and feed are high, but the high prices of live sea bass can bring good returns.
Sustainability: Marine cage farms need to be carefully managed to avoid environmental impacts (e.g. waste disposal, risk of escape).
In modern aquaculture systems, this cycle can be optimized through genetic selection, precision feeding and advanced water quality control.

Sturgeon

1. Selection and management (10-20 years and above, accelerated by the use of hormones)

Goal: Produce viable eggs and sperm for artificial reproduction.
Artificial broodstock:
Adult fish are selected from genetically healthy, fast-growing strains (e.g. Siberian sturgeon, Russian sturgeon, or white sturgeon × sterlet hybrids) to avoid reliance on wild populations.
It takes 8-15 years for females to reach sexual maturity (for caviar) naturally, but hormone therapy (e.g. gonadotropin-releasing hormone injections) can shorten this by 2-5 years, an innovation that is critical to economic viability.
Spawning induction:
Semen is collected from male fish and eggs are removed from female fish manually or surgically. Artificial insemination is the standard method to increase fertilization rates (80-90%).

2. Incubation stage (0-3 months)

Phase I: Egg incubation (3-10 days)
Incubation conditions: Eggs are incubated in clean, oxygen-rich water (15-18°C, pH 7.0-8.5) and placed in dedicated tanks or trays. The sticky eggs are gently agitated to prevent fungal growth.
Hatching: When the juveniles (1-2 cm) hatch, the yolk sac is removed from the yolk sac, which is responsible for nutrition and lasts for 1-2 weeks. Under controlled conditions, the survival rate of juveniles is over 90% (while the survival rate in wild conditions is less than 10%).
Phase II: First feeding and fry rearing (2-3 months)
Yolk sac absorption: After the yolk is exhausted, the fry switch to exogenous feeding. Initial feeding is 2-4 weeks, fed with live bait (rotifers, brine shrimp or copepods). Feed transition: Gradually introduce formulated pelleted feed (high protein, 40-50% crude protein, balanced amino acids and lipids) to reduce dependence on wild feed sources.
Water quality: Dissolved oxygen (≥6 mg/L) and water temperature (18-22 degrees Celsius) are strictly controlled to minimize stress and disease. Mechanical filtration and biological filtration systems are standard in recirculating aquaculture systems (RAS).

3. Juvenile fish growing stage (1-7 years)

Phase I: Juvenile rearing (1-3 years)
Rearing: Juveniles (5-10 cm) are reared in tanks, ponds or recirculating aquaculture systems (RAS) (often for biosecurity and water efficiency). Density varies by system:
Tanks: 10-20 kg/m3 with constant water flow to ensure oxygenation.
RAS: 30-50 kg/m3 with filters to recycle 90-95% of the water (reducing environmental impact).
Growth rate: Depends on species and feed:
Mostly carnivorous species (e.g. Russian sturgeon): 1-2 kg in 3-4 years.
Caviar-focused females: 5-10 kg in 5-7 years (to prepare for ovarian development).
Phase II: Subadult to adult maturity (caviar production takes 3-15 years)
Caviar production focus: Females are monitored by ultrasound to track ovarian development. In RAS (Reproducible Assimilation System), controlled photoperiod (12-14 h light) and stable temperature (18-20°C) can accelerate gonadal growth.
Feed optimization: Use high-quality pelleted feeds with added vitamins (e.g., vitamin E to promote reproductive health). Modern feeds are increasingly replacing fishmeal with plant proteins (soy, wheat gluten) to reduce the ecological footprint.

4. Harvesting and processing

a. Meat harvest (3-5 years)
When: When fish reach 1-3 kg (market size for fillets, steaks or smoked products). Harvest is by draining tanks/ponds and grading by size.
Processing: Fillets are refrigerated or frozen; by-products (skin, cartilage) can be used to make leather or supplements.
b. Caviar harvest (8-15 years for females)
Non-lethal extraction (modern practice): Removal of eggs without killing the fish is done through laparoscopic surgery or gentle abdominal massage, allowing the fish to spawn repeatedly (every 2-3 years). Survival rates after surgery exceed 90%.
Traditional lethal harvest:
Historically, female fish were euthanized to extract eggs, but this practice is decreasing due to the Sustainable Development Goals. The roe is graded by size (bonito: 3.5-4 mm; osietra: 2.5-3.5 mm) and color (from light gold to dark brown) and then salted (3-5% salt concentration) for preservation.

5. Key technologies and environmental control

Water quality management: Key parameters include dissolved oxygen (6-8 mg/L), ammonia ( < 0.02 mg/L), and nitrite ( < 0.1 mg/L). RAS systems use biofilters to convert toxic nitrogen compounds into safe nitrates.
Disease prevention: Quarantine of new fish species, vaccination (e.g., against sturgeon viral hemorrhagic syndrome), and the addition of probiotics to feed to boost immunity.
Genetic improvement: Selective breeding programs target traits such as rapid growth, early maturity, and high egg production (e.g., hybrid sturgeons grow 20-30% faster than purebred sturgeons).

6. Sustainability and Challenges

Shorter cycle times: Hybrids (such as the "Sevruga", a cross between a sterlet and a Russian sturgeon) mature 2-3 years earlier than pure white sturgeon, making caviar production more viable.
Environmental impact:
RAS systems use 90% less water than flow-through systems, but require a lot of energy for filtration and heating.
Plant-based feeds minimize reliance on wild fish (such as anchovies for fishmeal), reducing pressure on marine ecosystems.
Compliance: Farms must adhere to the guidelines of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), ensuring that no wild-caught genes are used in the breeding process.

Tuna

1. Egg laying and early development

Sexual maturity: Varies by species:
Yellowfin tuna: 3-5 years.
Bluefin tuna: 3-12 years (bluefin tuna may take up to 10 years to mature).
Spawning grounds: Warm tropical/subtropical oceans (e.g. Pacific, Indian and Atlantic). Females release millions of eggs (up to 10 million per spawning in large species) into the water column, which are fertilized externally by males.
Incubation: The eggs hatch in 24-48 hours, depending on water temperature (warmer water, faster development). Larvae are small (1-2 mm) and vulnerable to predators (e.g. other fish, plankton-feeding fish) and ocean currents.

2. Juvenile and juvenile stages

Juvenile stage (weeks to months):
Drifting with ocean currents, feeding on zooplankton. Rapid growth, but high mortality (estimated to be less than 1% survive to adulthood).
Morphological changes: development of fins, pigmentation, and transition from planktonic to active swimming.
Juvenile stage (1-5 years):
Adults form groups for self-defense and feeding. Diet shifts to small fish (e.g., anchovies, sardines), squid, and crustaceans.
Migration begins: Juveniles migrate to feeding grounds, avoiding extreme temperatures and seeking areas with abundant prey.

3. Adult stage and migration

Maturity and lifespan:
Adults can reach 1-2m (yellowfin) to 3m (bluefin) in length and live 15-20 years (some species, such as southern bluefin, can live up to 40 years).
Top predator: Feeds on fish (mackerel, herring), squid and jellyfish, and requires a high metabolic rate to maintain fast swimming (up to 70 km/h for some species).
Migration:
Migrate long distances for feeding and spawning (e.g. northern bluefin will cross the Atlantic to migrate between Europe and North America).
Seasonal pattern: Follows changes in prey and water temperature, making it highly adaptable but vulnerable to overfishing on predictable routes.

4. Human intervention: fishing and harvesting

Target stages:
Junior/subadult: 1-3 kg, caught for canned tuna (e.g. skipjack, yellowfin).
Adult/mature: 50-200 kg, caught for sashimi (e.g. bluefin, bigeye), larger individuals fetch higher prices.
Fishing methods:
Purse seine: works well for schooling fish (e.g. skipjack), but may catch dolphins or other bycatch.
Longline: targets large pelagic fish (bluefin, bigeye), but has high bycatch rates of turtles and seabirds.
Pole and line: more selective, used for skipjack in sustainable fisheries (e.g. Pacific Islands).
Regulations: International quotas (e.g. ICCAT quotas for Atlantic tuna) are designed to prevent overfishing, but illegal fishing and climate change threaten tuna stocks.

5. Environmental and human challenges

Climate change: Warming waters alter spawning grounds and prey availability.
Overfishing: Some species (e.g., East Atlantic bluefin tuna) face extinction, prompting tighter quotas and aquaculture initiatives.
Aquaculture: Farming of bluefin and yellowfin tuna is emerging, but challenges include high feed costs (dependence on wild fishmeal) and disease control.
Species-specific variation
Bluefin tuna: takes the longest to mature, has the highest commercial value, and is most vulnerable to overfishing.
Skipjack tuna: grows fastest (matures in 2 years), is most abundant, and dominates canned products.
Bigeye tuna: prefers deep water, is good for sashimi, and grows slower than yellowfin.
Conclusion
The tuna production cycle is a delicate balance between biological processes and human exploitation. Sustainable management—including science-based quotas, improved fishing gear to reduce bycatch, and the development of aquaculture—is essential to protecting tuna populations for future generations. Understanding species-specific cycles can help mitigate ecological impacts and ensure the economic viability of fisheries.

Other fish species

Aquaculture is one of the fastest growing sources of protein for people around the world seeking to diversify their diets. In key growing regions such as North America, Latin America, Asia, and Africa, we provide feed and nutritional products for a variety of aquaculture species, including:

Alligator, Baitfish, Barramundi
Bluegill, Carp, Catfish
Catfish, Cobia
Crab, Grey, Mullet
Eel, Flounder, Flatfish
Hilal, Shad, Golden, Pomfret
Grey, Mullet, Koi, Carp, Mackerel